Capacitive and ohmic terminals in a phase-change material (PCM) radio frequency (RF) switch

ABSTRACT

A radio frequency (RF) switch includes a phase-change material (PCM), a heating element underlying an active segment of the PCM and extending outward and transverse to the PCM, a capacitive RF terminal, and an ohmic RF terminal. The capacitive RF terminal can include a first trench metal liner situated on a first passive segment of the PCM, and a dielectric liner separating the first trench metal liner from a first trench metal plug. The ohmic RF terminal can include a second trench metal liner situated on a second passive segment of the PCM, and a second trench metal plug ohmically connected to the second trench metal liner. Alternatively, the capacitive RF terminal and the ohmic RF terminal can include lower metal portions and upper metal portions. A MIM capacitor can be formed by the upper metal portion of the capacitive RF terminal, an insulator, and a patterned top plate.

CLAIMS OF PRIORITY

This is a divisional of application Ser. No. 16/271,505 filed on Feb. 8,2019. application Ser. No. 16/271,505 filed on Feb. 8, 2019 (“the parentapplication”) is a continuation-in-part of and claims the benefit of andpriority to application Ser. No. 16/103,490 filed on Aug. 14, 2018,titled “Manufacturing RF Switch Based on Phase-Change Material,”. Theparent application is also a continuation-in-part of and claims thebenefit of and priority to application Ser. No. 16/103,587 filed on Aug.14, 2018. titled “Design for High Reliability RF Switch Based onPhase-Change Material,”. The parent application is also acontinuation-in-part of and claims the benefit of and priority toapplication Ser. No. 16/103,646 filed on Aug. 14, 2018, titled “PCM RFSwitch Fabrication with Subtractively Formed Heater,”. The parentapplication is further a continuation-in-part of and claims the benefitof and priority to application Ser. No. 16/114,106 filed on Aug. 27,2018, titled “Fabrication of Contacts in an RF Switch Having aPhase-Change Material (PCM) and a Heating Element,”. The parentapplication is also a continuation-in-part of and claims the benefit ofand priority to application Ser. No. 16/231,121 filed on Dec. 21, 2018,titled “Phase-Change Material (PCM) Radio Frequency (RF) Switches with.Capacitively Coupled RF Terminals,”. The disclosures and contents of allof the above-identified applications are hereby incorporated fully byreference into the parent application and the present divisionalapplication.

BACKGROUND

Phase-change materials (PCM) are capable of transforming from acrystalline phase to an amorphous phase. These two solid phases exhibitdifferences in electrical properties, and semiconductor devices canadvantageously exploit these differences. Given the ever-increasingreliance on radio frequency (RF) communication, there is particular needfor RF switching devices to exploit phase-change materials. However, thecapability of phase-change materials for phase transformation dependsheavily on how they are exposed to thermal energy and how they areallowed to release thermal energy. For example, in order to transforminto an amorphous state, phase-change materials may need to achievetemperatures of approximately seven hundred degrees Celsius (700° C.) ormore, and may need to cool down within hundreds of nanoseconds.

It is sometimes desirable to avoid fabricating only ohmic contacts forconnecting to RF terminals of a PCM RF switch. In those instances, arobust capacitive (and non-ohmic) contact can be a good choice. However,capacitance fabrication techniques applicable to conventionalsemiconductor devices may not be optimum for, or easily compatible with,PCM RF switches, and may not properly utilize or take advantage of theunique structure, layout, and geometry of PCM RF switches. Moreover, itis often desirable to have both ohmic and capacitive contacts forconnecting to RF terminals of PCM RF switches. As such, concurrentlyfabricating both capacitive and ohmic RF terminals in PCM RF switchescan present additional and significant manufacturing challenges.

Thus, there is a need in the art to reliably and concurrentlymanufacture both capacitive and ohmic RF terminals for PCM RF switches.

SUMMARY

The present disclosure is directed to concurrent fabrication of andstructure for capacitive terminals and ohmic terminals in a phase-changematerial (PCM) radio frequency (RF) switch, substantially as shown inand/or described in connection with at least one of the figures, and asset forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a portion of a flowchart of an exemplary method forconcurrently manufacturing both a capacitive radio frequency (RF)terminal and an ohmic RF terminal in a phase-change material (PCM) RFswitch according to one implementation of the present application.

FIG. 2 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 3 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 4 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 5 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 6 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 7 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 8 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 9 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 10 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 11 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 12 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 13 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 1 according to one implementation of the present application.

FIG. 14 illustrates a portion of a flowchart of an exemplary method forconcurrently manufacturing both a capacitive RF terminal and an ohmic RFterminal in a PCM RF switch according to one implementation of thepresent application.

FIG. 15 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 16 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 17 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 18 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 19 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 20 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 21 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

FIG. 22 illustrates a cross-sectional view of a portion of a PCM RFswitch structure processed in accordance with an action in the flowchartof FIG. 14 according to one implementation of the present application.

DETAILED DESCRIPTION

The following description contains specific information pertaining toimplementations in the present disclosure. The drawings in the presentapplication and their accompanying detailed description are directed tomerely exemplary implementations. Unless noted otherwise, like orcorresponding elements among the figures may be indicated by like orcorresponding reference numerals. Moreover, the drawings andillustrations in the present application are generally not to scale, andare not intended to correspond to actual relative dimensions.

FIG. 1 illustrates a portion of a flowchart of an exemplary method forconcurrently manufacturing both a capacitive radio frequency (RF)terminal and an ohmic RF terminal in a phase-change material (PCM) RFswitch according to one implementation of the present application.Certain details and features have been left out of the flowchart thatare apparent to a person of ordinary skill in the art. For example, anaction may consist of one or more sub-actions or may involve specializedequipment or materials, as known in the art. Moreover, some actions,such as masking and cleaning actions, are omitted so as not to distractfrom the illustrated actions. Actions 100 through 122 shown in theflowchart of FIG. 1 are sufficient to describe one implementation of thepresent inventive concepts, other implementations of the presentinventive concepts may utilize actions different from those shown in theflowchart of FIG. 1. Moreover, structures shown in FIGS. 2 through 13illustrate the results of performing respective actions 100 through 122in the flowchart of FIG. 1, respectively. For example, structure 200shows a PCM RF switch structure after performing action 100, structure222 shows a PCM RF switch structure after performing action 122, and soforth.

Referring to FIG. 2, PCM RF switch structure 200 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 100 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 2, PCMRF switch structure 200 includes substrate 224, lower dielectric 226,heating element 228, thermally conductive and electrically insulatinglayer 230, PCM 232 having active segment 234 and passive segments 236 aand 236 b, and optional contact uniformity support layer 238. PCM RFswitch structure 200 may include other structures not shown in FIG. 2.

Substrate 224 is situated under lower dielectric 226. In oneimplementation, substrate 224 is an insulator, such as silicon oxide(SiO₂). In various implementations, substrate 224 is a silicon (Si),silicon-on-insulator (SOI), sapphire, complementarymetal-oxide-semiconductor (CMOS), bipolar CMOS (BiCMOS), or group III-Vsubstrate. In various implementations, a heat spreader is integratedwith substrate 224, or substrate 224 itself performs as a heat spreader.Substrate 224 can have additional layers (not shown in FIG. 2). In oneimplementation, substrate 224 can comprise a plurality of interconnectmetal levels and interlayer dielectric layers. Substrate 224 can alsocomprise a plurality of devices, such as integrated passive devices(IPDs) (not shown in FIG. 2).

Lower dielectric 226 is situated on top of substrate 224, and isadjacent to the sides of heating element 228. In the presentimplementation, lower dielectric 226 extends along the width of RFswitch structure 200, and is also coplanar with heating element 228. Invarious implementations, lower dielectric 226 can have a relative widthand/or a relative thickness greater or less than shown in FIG. 2. Lowerdielectric 226 may comprise a material with thermal conductivity lowerthan that of thermally conductive and electrically insulating layer 230.In various implementations, lower dielectric 226 can comprise siliconoxide (SiO₂), silicon nitride (Si_(X)N_(Y)), or another dielectric.

Heating element 228 is situated in lower dielectric 226. Heating element228 also underlies active segment 234 of PCM 232. Heating element 228generates a crystallizing heat pulse or an amorphizing heat pulse fortransforming active segment 234 of PCM 232. Heating element 228 cancomprise any material capable of Joule heating. Preferably, heatingelement 228 comprises a material that exhibits minimal or substantiallyno electromigration, thermal stress migration, and/or agglomeration. Invarious implementations, heating element 228 can comprise tungsten (W),molybdenum (Mo), titanium (Ti), titanium nitride (TiN), titaniumtungsten (TiW), tantalum (Ta), nickel chromium (NiCr), or nickelchromium silicon (NiCrSi). For example, in one implementation, heatingelement 228 comprises tungsten lined with titanium and titanium nitride.Heating element 228 may be formed by a damascene process, a subtractiveetch process, or any other suitable process. Heating element 228 can beconnected to electrodes of a pulse generator (not shown in FIG. 2) thatgenerates a crystallizing current pulse or an amorphizing voltage orcurrent pulses.

Thermally conductive and electrically insulating layer 230 is situatedon top of heating element 228 and lower dielectric 226, and under PCM232 and, in particular, under active segment 234 of PCM 232. Thermallyconductive and electrically insulating layer 230 ensures efficient heattransfer from heating element 228 toward active segment 234 of PCM 232,while electrically insulating heating element 228 from PCM 232, andother neighboring structures. Thermally conductive and electricallyinsulating layer 230 can comprise any material with high thermalconductivity and high electrical resistivity. In variousimplementations, thermally conductive and electrically insulating layer230 can comprise aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)),beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), diamond, ordiamond-like carbon.

PCM 232 is situated on top of thermally conductive and electricallyinsulating layer 230. PCM 232 also overlies heating element 228. PCM 232includes active segment 234 and passive segments 236 a and 236 b. Activesegment 234 of PCM 232 approximately overlies heating element 228 and isapproximately defined by heating element 228. Passive segments 236 a and236 b of PCM 232 extend outward and are transverse to heating element228. As used herein, “active segment” refers to a segment of PCM thattransforms between crystalline and amorphous states, for example, inresponse to a crystallizing or an amorphizing heat pulse generated byheating element 228, whereas “passive segment” refers to a segment ofPCM that does not make such transformation and maintains a crystallinestate (i.e., maintains a conductive state). With proper heat pulses andheat dissipation, active segment 234 of PCM 232 can transform betweencrystalline and amorphous states, allowing RF switch structure 200 toswitch between ON and OFF states respectively.

PCM 232 can be germanium telluride (Ge_(X)Te_(Y)), germanium antimonytelluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), orany other chalcogenide. In various implementations, PCM 232 can begermanium telluride having from forty percent to sixty percent germaniumby composition (i.e., Ge_(X)Te_(Y), where 0.4≤X≤0.6 and Y=1−X). Thematerial for PCM 232 can be chosen based upon ON state resistivity, OFFstate electric field breakdown threshold, crystallization temperature,melting temperature, or other considerations. PCM 232 can be provided,for example, by physical vapor deposition (PVD), sputtering, chemicalvapor deposition (CVD), evaporation, or atomic layer deposition (ALD).In one implementation, PCM 232 can have a thickness of approximatelyfive hundred angstroms to approximately two thousand angstroms (500Å-2000 Å). In other implementations, PCM 232 can have any otherthicknesses. The thickness of PCM 232 can be chosen based upon sheetresistance, crystallization power, amorphization power, or otherconsiderations. It is noted that in FIG. 2, current flowing in heatingelement 228 flows substantially under active segment 234 of PCM 232.

Optional contact uniformity support layer 238 is situated over PCM 232.In one implementation, optional contact uniformity support layer 238comprises Si_(X)N_(Y). In another implementation, optional contactuniformity support layer 238 is a bi-layer that comprises oxide andnitride, such as SiO₂ under Si_(X)N_(Y). Optional contact uniformitysupport layer 238 can be provided, for example, by plasma enhanced CVD(PECVD) or high density plasma CVD (HDP-CVD). In one implementation,optional contact uniformity support layer 238 can have a thickness ofapproximately fifty angstroms to approximately one thousand two hundredand fifty angstroms (50 Å-1250 Å). By forming optional contactuniformity support layer 238 as shown in FIG. 2, PCM 232 will remainsubstantially intact, and uniform contact can be made to passivesegments 236 a and 236 b of PCM 232, as described below. Optionalcontact uniformity support layer 238 is optional in that the inventiveconcepts of the present application may be implemented without formingoptional contact uniformity support layer 238, as described below.

Referring to FIG. 3, PCM RF switch structure 202 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 102 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 3, RFterminal dielectric 240 is formed over PCM 232 and over optional contactuniformity support layer 238 (in case optional contact uniformitysupport layer 238 is used). RF terminal dielectric 240 is also formedover thermally conductive and electrically insulating layer 230. In thepresent implementation, chemical machine polishing (CMP) is used toplanarize RF terminal dielectric 240. In various implementations, RFterminal dielectric 240 is SiO₂, Si_(X)N_(Y), or another dielectric. RFterminal dielectric 240 can be formed, for example, by PECVD or HDP-CVD.In one implementation, the deposition thickness of RF terminaldielectric 240 can range from approximately one half a micron toapproximately two microns (0.5 μm-2 μm). In one implementation, athickness of RF terminal dielectric 240 is significantly greater than athickness of optional contact uniformity support layer 238.

Referring to FIG. 4, PCM RF switch structure 204 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 104 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 4,trenches or holes 242 a and 242 b are etched in RF terminal dielectric240 and in optional contact uniformity support layer 238 (in caseoptional contact uniformity support layer 238 is used). Trenches orholes 242 a and 242 b extend to passive segment 236 a and 236 brespectively of PCM 232.

In the present implementation, forming trenches 242 a and 242 b maycomprise two different etching actions. In the first etching action, RFterminal dielectric 240 can be aggressively etched without having toaccurately time the etching action. This etching action can use aselective etch, for example, a fluorine-based plasma dry etch, andoptional contact uniformity support layer 238 can perform as an etchstop while RF terminal dielectric 240 is selectively etched. In thesecond etching action, optional contact uniformity support layer 238 ispunch-through etched. As used herein, “punch-through” refers to a shortetching action that can be accurately timed to stop at the top surfaceof PCM 232. In RF switch structure 204, trenches 242 a and 242 b arenarrow and optional contact uniformity support layer 238 is thin. Thus,only a small volume of optional contact uniformity support layer 238 isetched, and the punch-through etching action is short and can beaccurately timed. In one implementation, a chlorine-based plasma dryetch is used for this etching action.

Optional contact uniformity support layer 238 is optional in that theinventive concepts of the present application may be implemented withoutoptional contact uniformity support layer 238, and trenches 242 a and242 b can extend through RF terminal dielectric 240 into PCM 232.Because the ON state resistance (R_(ON)) of an RF switch depends heavilyon the uniformity of contact made with PCM 232, the R_(ON) will besignificantly lower when optional contact uniformity support layer 238is used.

Referring to FIG. 5, PCM RF switch structure 206 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 106 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 5, metalliner 244 is formed in trenches 242 a and 242 b, and on passive segments236 a and 236 b of PCM 232. Metal liner 244 lines trenches 242 a and 242b without completely filling trenches 242 a and 242 b. Metal liner 244is also formed over RF terminal dielectric 240. In variousimplementations, metal liner 244 can comprise tungsten (W), molybdenum(Mo), titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW),tantalum (Ta), cobalt (Co), nickel (Ni), nickel chromium (NiCr), ornickel chromium silicon (NiCrSi). For example, in one implementation,metal liner 244 comprises cobalt lined with titanium nitride andtungsten. Metal liner 244 may be formed by PVD, CVD, or any othersuitable process.

Referring to FIG. 6, PCM RF switch structure 208 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 108 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 6,trench metal liners 246 a and 246 b are formed in trenches 242 a and 242b respectively and on passive segments 236 a and 236 b respectively ofPCM 232. Thus, trench metal liners 246 a and 246 b are ohmicallyconnected to passive segments 236 a and 236 b respectively of PCM 232.In the present implementation, trench metal liners 246 a and 246 b areformed by removing a middle segment of metal liner 244 (shown in FIG. 5)on RF terminal dielectric 240 between trenches 242 a and 242 b, forexample, using a chlorine based reactive ion etch (RIE). Outside trench242 a, trench metal liner extension 246 x is situated over RF terminaldielectric 240 and integrally connected to trench metal liner 246 a.

Referring to FIG. 7, PCM RF switch structure 210 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 110 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 7,dielectric liner 248 is formed on trench metal liners 246 a and 246 b intrenches 242 a and 242 b. Dielectric liner 248 is also formed on trenchmetal liner extension 246 x and on RF terminal dielectric 240.Dielectric liner 248 lines trench metal liners 246 a and 246 b. In oneimplementation, dielectric liner 248 is silicon nitride. In variousimplementations, dielectric liner 248 is a high-k dielectric, such astantalum pentoxide, aluminum oxide, hafnium oxide, zirconium oxide,zirconium aluminum silicate, hafnium silicate, hafnium aluminum silicateor another dielectric with a relatively high dielectric constant. In oneimplementation, the thickness of dielectric liner 248 can range fromapproximately two hundred angstroms to approximately six hundredangstroms (200 Å-600 Å). As further shown in FIG. 7, dielectric linerextension 248 x is situated over trench metal liner extension 246 x andintegrally connected to dielectric liner 248.

Referring to FIG. 8, PCM RF switch structure 212 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 112 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 8,dielectric liner 248 is removed from trench metal liner 246 b. In oneimplementation, a fluorine based RIE is used to remove dielectric liner248 from trench metal liner 246 b. Dielectric liner 248 remains ontrench metal liner 246 a. Notably, dielectric liner 248 remains withoverplot 250 relative to trench metal liner 246 a. Overplot 250 protectsagainst shorting, as described below. Outside trench 242 a, dielectricliner extension 248 x is situated over trench metal liner extension 246x and integrally connected to dielectric liner 248.

Referring to FIG. 9, PCM RF switch structure 214 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 114 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 9, metal252 is deposited on dielectric liner 248 in trench 242 a, and on trenchmetal liner 246 b in trench 242 b. Metal 252 fills trenches 242 a and242 b. In various implementations, metal 252 can comprise aluminum (Al),copper (Cu), titanium (Ti), or titanium nitride (TiN). For example, inone implementation, metal 252 comprises a sequential stack of titanium,titanium nitride, aluminum, titanium, and titanium nitride. Metal 252can be formed by PVD, or any other suitable process. In oneimplementation, the deposition thickness of metal 252 can beapproximately one half a micron (0.5 μm).

Referring to FIG. 10. PCM RF switch structure 216 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 116 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 10,trench metal plug 254 a is formed in trench 242 a on dielectric liner248, and trench metal plug 254 b and is formed in trench 242 b on trenchmetal liner 246 b, thereby substantially completing capacitive RFterminal 256 a and ohmic RF terminal 256 b of PCM RF switch structure216. Capacitive RF terminal 256 a and ohmic RF terminal 256 b provide RFsignals to/from passive segments 236 a and 236 b respectively of PCM232. Capacitive RF terminal 256 a includes trench metal liner 246 a,dielectric liner 248, and trench metal plug 254 a that together form atrench capacitor. Dielectric liner 248 separates trench metal liner 246a from trench metal plug 254 a. As such, trench metal liner 246 a isohmically separated from, but capacitively coupled to trench metal plug254 a. Ohmic RF terminal 256 b includes trench metal liner 246 b andtrench metal plug 254 b. Unlike trench metal liner 246 a and trenchmetal plug 254 a of capacitive RF terminal 256 a, trench metal liner 246b and trench metal plug 254 b of ohmic RF terminal 256 b are ohmicallycoupled.

Capacitive RF terminal 256 a also includes trench metal liner extension246 x, dielectric liner extension 248 x, and trench metal plug extension254 x that further capacitively couple trench metal liner 246 a totrench metal plug 254 a. Trench metal liner extension 246 x, dielectricliner extension 248 x, and trench metal plug extension 254 x areoptional in that the inventive concepts of the present application maybe implemented without them, and trench metal liner 246 a would stillcapacitively couple to trench metal plug 254 a. However, capacitivecoupling between trench metal liner 246 a and trench metal plug 254 a isstrengthened when trench metal liner extension 246 x, dielectric linerextension 248 x, and trench metal plug extension 254 x are used.Although trench metal liner 246 a, dielectric liner 248, and trenchmetal plug 254 a are illustrated as integrally formed with trench metalliner extension 246 x, dielectric liner extension 248 x, and trenchmetal plug extension 254 x respectively, in one implementation they maybe different formations. For example, trench metal plug 254 a may besituated in trench 242 a and a metal may be subsequently formed overtrench metal plug 254 a to form trench metal plug extension 254 x. Inthis example, trench metal plug 254 a can comprise W, and trench metalplug extension 254 x can comprise Al or Cu.

In the present implementation, trench metal plugs 254 a and 254 b areformed by removing a middle segment of metal 252 (shown in FIG. 9)between trenches 242 a and 242 b, for example, using a metal etch.Notably, dielectric liner 248 remains with underplot 258 relative totrench metal liner 246 a. Underplot 258 protects against breakdown, asdescribed below. Outside trench 242 a, trench metal plug extension 254 xis situated over dielectric liner extension 248 x and integrallyconnected to trench metal plug 254 a.

Referring to FIG. 11, PCM RF switch structure 218 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 118 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 11,interlayer dielectric 260 is formed over trench metal plugs 254 a and254 b. In the present implementation, CMP is used to planarizeinterlayer dielectric 260. Interlayer dielectric 260 provides insulationbetween trench metal plugs 254 a and 254 b and subsequently formed viasor interconnect metal (not shown in FIG. 11). In variousimplementations, interlayer dielectric 260 is SiO₂, Si_(X)N_(Y), oranother dielectric. Interlayer dielectric 260 can be formed, forexample, by PECVD or HDP-CVD. In one implementation, the depositionthickness of RF terminal dielectric 240 can be approximately one half amicron (0.5 μm).

Referring to FIG. 12, PCM RF switch structure 220 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 120 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 12,interconnect holes 262 a and 262 b are etched in interlayer dielectric260. Interconnect holes 262 a and 262 b extend to trench metal plugs 254a and 254 b respectively. In the present implementation, trench metalplug 254 b of ohmic RF terminal 256 b is situated lower in PCM RF switchstructure 220 relative to trench metal plug 254 a of capacitive RFterminal 256 a, and interconnect hole 262 b is deeper than interconnecthole 262 a because capacitive RF terminal 256 a includes dielectricliner 248. Interconnect holes 262 a and 262 b in interlayer dielectric260 are selectively etched so that trench metal plug 254 a of capacitiveRF terminal 256 a remains substantially undamaged while deeperinterconnect hole 262 b is etched.

Referring to FIG. 13, PCM RF switch structure 222 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 122 in the flowchart of FIG. 1 according toone implementation of the present application. As shown in FIG. 13,interconnect metals 264 a and 264 b are formed in interconnect holes 262a and 262 b (labeled in FIG. 12) respectively and on trench metal plugs254 a and 254 b respectively. In one implementation, a metal layer isdeposited over interlayer dielectric 260 and in interconnect holes 262 aand 262 b (labeled in FIG. 12) over trench metal plugs 254 a and 254 b,and then a middle segment thereof between interconnect holes 262 a and262 b (labeled in FIG. 12) is etched, thereby forming interconnectmetals 264 a and 264 b. Interconnect metals 264 a and 264 b can be partof routing interconnects for routing electrical signals betweencapacitive RF terminal 256 a or ohmic RF terminal 256 b and variousdevices (not shown in FIG. 13) that may exist independent of PCM RFswitch structure 222. In various implementations, interconnect metals264 a and 264 b can comprise Al and/or Cu. Interconnect metals 264 a and264 b can be formed by PVD, or any other suitable process. In oneimplementation, the thickness of interconnect metals 264 a and 264 b canbe approximately three microns (3 μm). In various implementations, PCMRF switch structure 222 can include more interconnect metals and/or moreinterlayer dielectrics than those shown in FIG. 13.

PCM RF switch structure 222 in FIG. 13 including one capacitive RFterminal 256 a and one ohmic RF terminal 256 b, and manufacturedaccording to the flowchart in FIG. 1, provides several advantages.First, the trench capacitor of capacitive RF terminal 256 a capacitivelycouples trench metal liner 246 a to trench metal plug 254 a, creatingpart of an RF signal path of PCM RF switch structure 222, despite thatpatterned trench metal liner 246 a and trench metal plug 254 a areohmically separated from each other. Second, because capacitive RFterminal 256 a is directly connected to PCM 232 without any traces orinterconnects, such as interconnect metals 264 a and 264 b interveningtherebetween, routing resistance is lowered and the quality factor ofthe trench capacitor is high. Third, because PCM RF switch structure 222in FIG. 13 includes one capacitive RF terminal 256 a and one ohmic RFterminal 256 b, two capacitive terminals are not placed in series in theRF signal path, and thus, do not halve the total capacitance of theswitch. Fourth, compared to a manufacturing process that forms twocapacitive RF terminals, a manufacturing process of the presentapplication needs only a few additional steps to form one capacitive RFterminal 256 a and one ohmic RF terminal 256 b.

Fifth, overplot 250 of dielectric liner 248 protects capacitive RFterminal 256 a against shorting. A natural result of etching metal 252(shown in FIG. 9) to form trench metal plugs 254 a and 254 b (shown inFIG. 10) is that stringers will form at an edge of trench metal plug 254a and undesirably short to trench metal liner 246 a, which would resultin “capacitive” RF terminal 256 a not forming a capacitor. Overplot 250of dielectric liner 248 intervenes between the edge of trench metal plug254 a and trench metal liner 246 a. Because dielectric liner 248provides electrical insulation, a stringer would not couple to trenchmetal liner 246 a and would not cause a short.

Sixth, underplot 258 of trench metal plug 254 a protects capacitive RFterminal 256 a against breakdown. Dielectric liner 248 usually exhibitssome defects or abnormalities near the sharp corner at the edge oftrench metal liner 246 a, which would undesirably result in breakdownvariations for the trench capacitor of capacitive RF terminal 256 a.Underplot 258 of trench metal plug 254 a ensures that trench metal plug254 a is not situated over a sharp corner of dielectric liner 248. Assuch, breakdown of capacitive RF terminal 256 a is more preciselycontrolled, and PCM RF switch structure 222 is more reliable.

Seventh, because PCM RF switch structure 222 utilizes trench metalliners 246 a and 246 b and trench metal plugs 254 a and 254 b intrenches 242 a and 242 b, more interface area is available tocapacitively couple, and capacitance value of capacitive RF terminal 256a is increased. Eighth, because PCM RF switch structure 222 utilizes athin high-k dielectric liner 248, the capacitive coupling between trenchmetal liner 246 a and trench metal plug 254 a is significantlyincreased. Ninth, because PCM RF switch structure 222 utilizes overhangregions, capacitive coupling between trench metal liner 246 a and trenchmetal plug 254 a is further increased.

FIG. 14 illustrates a portion of a flowchart of an exemplary method forconcurrently manufacturing both a capacitive RF terminal and an ohmic RFterminal in a PCM RF switch according to one implementation of thepresent application. Certain details and features have been left out ofthe flowchart that are apparent to a person of ordinary skill in theart. For example, an action may consist of one or more sub-actions ormay involve specialized equipment or materials, as known in the art.Moreover, some actions, such as masking and cleaning actions, areomitted so as not to distract from the illustrated actions. Actions 166through 180 shown in the flowchart of FIG. 14 are sufficient to describeone implementation of the present inventive concepts, otherimplementations of the present inventive concepts may utilize actionsdifferent from those shown in the flowchart of FIG. 14. Moreover,structures shown in FIGS. 15 through 22 illustrate the results ofperforming respective actions 166 through 180 in the flowchart of FIG.14, respectively. For example, structure 266 shows a PCM RF switchstructure after performing action 166, structure 280 shows a PCM RFswitch structure after performing action 180, and so forth.

Referring to FIG. 15, PCM RF switch structure 266 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 166 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 15, PCMRF switch structure 266 includes substrate 224, lower dielectric 226,heating element 228, thermally conductive and electrically insulatinglayer 230, PCM 232 having active segment 234 and passive segments 236 aand 236 b, optional contact uniformity support layer 238, RF terminaldielectric 240, and trenches 242 a and 242 b. Action 166 in theflowchart of FIG. 14 generally corresponds to actions 100, 102, and 104in the flowchart of FIG. 1. Accordingly, PCM RF switch structure 266 inFIG. 15 generally corresponds to PCM RF switch structure 204 in FIG. 4,and may have any implementations and advantages described above.

Referring to FIG. 16, PCM RF switch structure 268 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 168 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 16,lower metal portions 282 a and 282 b are formed in trenches 242 a and242 b (shown in FIG. 15), and on passive segments 236 a and 236 b of PCM232. Thus, lower metal portions 282 a and 282 b are ohmically connectedto passive segments 236 a and 236 b respectively of PCM 232. Notably,lower metal portions 282 a and 282 b fill trenches 242 a and 242 b. Inone implementation, lower metal portions 282 a and 282 b can be formedby depositing a metal, for example, using PVD, CVD, or any othersuitable process, and then polishing the metal, for example, using CMP.In another implementation, lower metal portions 282 a and 282 b can beformed by a damascene process. In various implementations, lower metalportions 282 a and 282 b can comprise tungsten (W), aluminum (Al),copper (cu), molybdenum (Mo), titanium (Ti), titanium nitride (TiN),titanium tungsten (TiW), tantalum (Ta), cobalt (Co), nickel (Ni), nickelchromium (NiCr), or nickel chromium silicon (NiCrSi).

Referring to FIG. 17, PCM RF switch structure 270 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 170 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 17,metal layer 284 is formed on lower metal portions 282 a and 282 b, andon RF terminal dielectric 240. In various implementations, metal layer284 can comprise aluminum (Al), copper (Cu), titanium (Ti), or titaniumnitride (TiN). For example, in one implementation, metal layer 284comprises a sequential stack of titanium, titanium nitride, aluminum,titanium, and titanium nitride. In the present implementation, metallayer 284 is substantially planar. Metal layer 284 can be formed by PVD,or any other suitable process. In one implementation, the thickness ofmetal layer 284 can be approximately one half a micron (0.5 μm).

Referring to FIG. 18. PCM RF switch structure 272 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 172 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 18,insulator 286 is formed on metal layer 284. In one implementation,insulator 286 is silicon nitride. In various implementations, insulator286 is a high-k dielectric, such as tantalum pentoxide, aluminum oxide,hafnium oxide, zirconium oxide, zirconium aluminum silicate, hafniumsilicate, hafnium aluminum silicate or another dielectric with arelatively high dielectric constant. In the present implementation,insulator 286 is substantially planar. Insulator 286 can be formed, forexample, by PECVD or HDP-CVD. In one implementation, the thickness ofinsulator 286 can range from approximately two hundred angstroms toapproximately six hundred angstroms (200 Å-600 Å).

Referring to FIG. 19, PCM RF switch structure 274 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 174 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 19, topmetal 288 is formed on insulator 286. In various implementations, topmetal 288 can comprise can comprise titanium nitride (TiN), tantalumnitride (TaN), or a stack comprising aluminum and titanium nitride ortantalum nitride. In the present implementation, top metal 288 issubstantially planar. Top metal 288 can be formed by PVD, or any othersuitable process. In one implementation, the thickness of top metal 288can range from approximately five hundred angstroms to approximately onethousand angstroms (500 Å-1000 Å).

Referring to FIG. 20. PCM RF switch structure 276 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 176 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 20, topmetal 288 (labeled in FIG. 19) is etched to form patterned top plate290. Top metal 288 (labeled in FIG. 19) is etched overlying lower metalportion 282 b, but remains overlying lower metal portion 282 a, therebyforming patterned top plate 290. In the present implementation,insulator 286 is partially etched. In another implementation insulator286 may remain substantially unetched.

Referring to FIG. 21, PCM RF switch structure 278 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 178 in the flowchart of FIG. 14 according toone implementation of the present application. As shown in FIG. 21,metal layer 284 (labeled in FIG. 20) is etched to form upper metalportions 292 a and 292 b, thereby forming metal-insulator-metal (MIM)capacitor 296 by upper metal portion 292 a, insulator 286, and patternedtop plate 290. Etching metal layer 284 to form upper metal portions 292a and 292 b also thereby substantially completes capacitive RF terminal294 a and ohmic RF terminal 294 b of PCM RF switch structure 278.Capacitive RF terminal 294 a and ohmic RF terminal 294 b provide RFsignals to/from passive segments 236 a and 236 b respectively of PCM232. Capacitive RF terminal 294 a includes lower metal portion 282 a,upper metal portion 292 a, insulator 286, and patterned top plate 290.Ohmic RF terminal 294 b includes lower metal portion 282 b and uppermetal portion 292 b.

In the present implementation, upper metal portions 292 a and 292 b areformed by removing a middle segment of metal layer 284 (labeled in FIG.20) between lower metal portions 282 a and 282 b, for example, using achlorine based RIE. In an alternative implementation, a single damasceneprocess can be used to form upper metal portions 292 a and 292 b priorto depositing insulator 286. Moreover, although lower metal portions 282a and 282 b and upper metal portions 292 a and 292 b are separateformations in FIG. 21, in other implementations they may be parts of thesame formation. For example, lower metal portions 282 a and 282 b andupper metal portions 292 a and 292 b can be formed as a single metalusing a dual damascene process. As another example, lower metal portions282 a and 282 b and upper metal portions 292 a and 292 b can be formedas a single metal by depositing a metal layer in trenches 242 a and 242b (labeled in FIG. 15) and over RF terminal dielectric 240, and thenetching a middle segment thereof between trenches 242 a and 242 b. Inthese examples, lower metal portions 282 a and 282 b and upper metalportions 292 a and 292 b would not have a boundary interface. Althoughupper metal portions 292 a and 292 b have overplots relative to lowermetal portions 282 a and 282 b in FIG. 21, in various implementations,upper metal portions 292 a and 292 b can be aligned with lower metalportions 282 a and 282 b, or can have underplots relative to lower metalportions 282 a and 282 b.

Referring to FIG. 22, PCM RF switch structure 280 illustrates across-sectional view of a portion of a PCM RF switch structure processedin accordance with action 180 in the flowchart of FIG. 14 according toone implementation of the present application. Action 180 in theflowchart of FIG. 14 generally corresponds to actions 118, 120, and 122in the flowchart of FIG. 1, and interlayer dielectric 260 andinterconnect metals 264 a and 264 b in FIG. 22 generally correspond tointerlayer dielectric 260 and interconnect metals 264 a and 264 b inFIG. 13, except for differences described below.

As shown in FIG. 22, interlayer dielectric 260 is formed over patternedtop plate 290 of capacitive RF terminal 294 a and over upper metalportion 292 b of ohmic RF terminal 294 b. Thus, patterned top plate 290of MIM capacitor 296 is situated within interlayer dielectric 260. Asused herein, “MIM capacitor” refers to a capacitor having a top plateformed within an interlayer dielectric where conventionally no metal(other than via or interconnect metal) exists, such as within interlayerdielectric 260.

Interconnect metal 264 a is formed in an interconnect hole etched ininterlayer dielectric 260, and on patterned top plate 290 of capacitiveRF terminal 294 a. Interconnect metal 264 b is formed in an interconnecthole etched in both interlayer dielectric 260 and insulator 286, and onupper metal portion 292 b of ohmic RF terminal 294 b. In contrast to PCMRF switch structure 222 in FIG. 13 where interconnect metals 264 a and264 b is connected to trench metal plugs 254 a and 254 b for capacitiveRF terminal 256 a and ohmic RF terminal 256 b, in PCM RF switchstructure 280 in FIG. 22, interconnect metal 264 b is connected to uppermetal portion 292 b of ohmic RF terminal 294 b, while interconnect metal264 a is connected to patterned top plate 290 of capacitive RF terminal294 a.

In the present implementation, upper metal portion 292 b of ohmic RFterminal 294 b is situated lower in PCM RF switch structure 280 relativeto patterned top plate 290 of capacitive RF terminal 294 a, andinterconnect metal 264 b extends deeper than interconnect metal 264 a,because capacitive RF terminal 294 a includes patterned top plate 290.Patterned top plate 290 of capacitive RF terminal 294 a can perform asan etch stop while interlayer dielectric 260 and insulator 286 areselectively etched, so that patterned top plate 290 of capacitive RFterminal 294 a remains substantially undamaged when deeper interconnectmetal 264 b is formed.

PCM RF switch structure 280 in FIG. 22 provides advantages similar toPCM RF switch structure 222 in FIG. 13 in that PCM RF switch structure280 in FIG. 22 includes one capacitive RF terminal 294 a and one ohmicRF terminal 294 b for providing RF signals to/from passive segments 236a and 236 b respectively of PCM 232. As described above, first, MIMcapacitor 296 of capacitive RF terminal 294 a capacitively couplespatterned top plate 290 to upper metal portion 292 a, creating part ofan RF signal path of PCM RF switch structure 280, despite the fact thatpatterned top plate 290 and upper metal portion 292 a are ohmicallyseparated from each other. Second, because capacitive RF terminal 294 ais directly connected to PCM 232 without any traces or interconnectsintervening therebetween, routing resistance is lowered and the qualityfactor of MIM capacitor 296 is high. Third, because PCM RF switchstructure 280 in FIG. 22 includes one capacitive RF terminal 294 a andone ohmic RF terminal 294 b, two capacitive terminals are not placed inseries in the RF signal path, and thus, do not halve the totalcapacitance of the switch. Fourth, compared to a manufacturing processthat forms two capacitive RF terminals, a manufacturing process of thepresent application needs only a few additional steps to form onecapacitive RF terminal 294 a and one ohmic RF terminal 294 b.

Additionally, PCM RF switch structure 280 in FIG. 22 provides severaladvantages over PCM RF switch structure 222 in FIG. 13. First, becauseinsulator 286 is only partially etched or substantially unetched afteretching of patterned top plate 290, there is little or no increase inleakage current of MIM capacitor 296 and little or no decrease in thebreakdown voltage of MIM capacitor 296 due to an increase in defects orvoids within insulator 286. As such, the capacitance value of MIMcapacitor 296 is more precisely controlled, and PCM RF switch structure280 is more reliable.

Second, in contrast to trench metal liners 246 a and 246 b in PCM RFswitch structure 220 in FIG. 12, lower metal portions 282 a and 282 b ofPCM RF switch structure 280 in FIG. 22 completely fill trenches.Accordingly metal layer 284, insulator 286, and top metal 288 (labeledin FIG. 19) can be formed substantially planar. Manufacturing issimplified. And compared to dielectric liner 248 in FIG. 13 that hasvarying thickness in trenches 242 a, insulator 286 has more uniformthickness, resulting in less breakdown variations for the MIM capacitor296 of capacitive RF terminal 294 a.

Third, MIM capacitor 296 formed by upper metal portion 292 a, insulator286, and patterned top plate 290 has a capacitance with significantlyimproved density. MIM capacitor 296 does not require addition ofinterlayer metal levels, and also does not use up lateral die space. MIMcapacitor 296 advantageously increases routing capability because MIMcapacitor 296 utilizes the space amply available between interlayerdielectrics, such as interlayer dielectric 260.

Thus, various implementations of the present application achieve amethod of concurrently manufacturing and a structure of a PCM RF switchhaving both capacitive and ohmic RF terminals that overcome thedeficiencies in the art while preserving or improving RF performance.

From the above description it is manifest that various techniques can beused for implementing the concepts described in the present applicationwithout departing from the scope of those concepts. For example, asingle capacitor can be formed in the RF path near one RF terminal,while the other RF terminal only employs ohmic connections. Moreover,while the concepts have been described with specific reference tocertain implementations, a person of ordinary skill in the art wouldrecognize that changes can be made in form and detail without departingfrom the scope of those concepts. As such, the described implementationsare to be considered in all respects as illustrative and notrestrictive. It should also be understood that the present applicationis not limited to the particular implementations described above, butmany rearrangements, modifications, and substitutions are possiblewithout departing from the scope of the present disclosure.

The invention claimed is:
 1. A radio frequency (RF) switch comprising: aphase-change material (PCM) and a heating element underlying an activesegment of said PCM and extending outward and transverse to said PCM; afirst RF terminal comprising a first lower metal portion connected to afirst upper metal portion; a MIM capacitor formed by said first uppermetal portion, an insulator, and a patterned top plate; said first lowermetal portion being ohmically connected to a first passive segment ofsaid PCM; a second RF terminal comprising a second lower metal portionconnected to a second upper metal portion; said second lower metalportion being ohmically connected to a second passive segment of saidPCM.
 2. The RF switch of claim 1, wherein said patterned top plate issituated within an interlayer dielectric.
 3. The RF switch of claim 1,further comprising a first interconnect metal ohmically connected tosaid patterned top plate, and a second interconnect metal ohmicallyconnected to said second upper metal portion.
 4. A method formanufacturing a capacitive RF terminal and an ohmic RF terminal in a PCMRF switch, said method comprising: forming a first lower metal portionfor said capacitive RF terminal and a second lower metal portion forsaid ohmic RF terminal; forming a metal layer on said first and secondlower metal portions; forming an insulator on said metal layer; forminga top metal on said insulator, etching said top metal so as to form apatterned top plate for said capacitive RF terminal; etching said metallayer so as to form a first upper metal portion for said capacitive RFterminal and a second upper metal portion for said ohmic RF terminal,thereby forming a MIM capacitor by said first upper metal portion, saidinsulator, and said patterned top plate.
 5. The method of claim 4,wherein said patterned top plate is situated within an interlayerdielectric.
 6. The method of claim 4, further comprising forming a firstinterconnect metal ohmically connected to said patterned top plate, anda second interconnect metal ohmically connected to said second uppermetal portion.
 7. The method of claim 4, wherein said first lower metalportion is ohmically connected to a first passive segment of a PCM, andsaid second lower metal portion is ohmically connected to a secondpassive segment of said PCM.
 8. The RF switch of claim 1, wherein saidPCM is selected from the group consisting of germanium telluride(Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)),germanium selenide (Ge_(X)Se_(Y)), and any other chalcogenide.
 9. The RFswitch of claim 1, wherein said heating element comprises materialselected from the group consisting of tungsten (W), molybdenum (Mo),titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW), tantalum(Ta), nickel chromium (NiCr), and nickel chromium silicon (NiCrSi). 10.The RF switch of claim 1, further comprising a thermally conductive andelectrically insulating layer situated between said heating element andsaid PCM.
 11. The RF switch of claim 10, wherein said thermallyconductive and electrically insulating layer comprises material selectedfrom the group consisting of comprise aluminum nitride (AlN), aluminumoxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), silicon carbide(SiC), diamond, and diamond-like carbon.
 12. The method of claim 7,wherein said PCM is selected from the group consisting of germaniumtelluride (Ge_(X)Te_(Y)), germanium antimony telluride(Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), and any otherchalcogenide.
 13. The method of claim 7, wherein said PCM RF switchcomprises a heating element underlying an active segment of said PCM.14. The method of claim 13, wherein said heating element comprisesmaterial selected from the group consisting of tungsten (W), molybdenum(Mo), titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW),tantalum (Ta), nickel chromium (NiCr), and nickel chromium silicon(NiCrSi).
 15. The method of claim 13, further comprising a thermallyconductive and electrically insulating layer situated between saidheating element and said PCM.
 16. A radio frequency (RF) switchcomprising: a phase-change material (PCM) and a heating elementunderlying an active segment of said PCM; a first RF terminalcapacitively coupled to a first passive segment of said PCM, said firstRF terminal comprising an MIM capacitor; a second RF terminal ohmicallyconnected to a second passive segment of said PCM; wherein saidcapacitively coupled first RF terminal and said ohmically connectedsecond RF terminal are both situated on a same side of said PCM.
 17. TheRF switch of claim 16, wherein said PCM is selected from the groupconsisting of germanium telluride (Ge_(X)Te_(Y)), germanium antimonytelluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), andany other chalcogenide.
 18. The RF switch of claim 16, wherein saidheating element comprises material selected from the group consisting oftungsten (W), molybdenum (Mo), titanium (Ti), titanium nitride (TiN),titanium tungsten (TiW), tantalum (Ta), nickel chromium (NiCr), andnickel chromium silicon (NiCrSi).
 19. The RF switch of claim 16, furthercomprising a thermally conductive and electrically insulating layersituated between said heating element and said PCM.
 20. The RF switch ofclaim 19, wherein said thermally conductive and electrically insulatinglayer comprises material selected from the group consisting of comprisealuminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide(Be_(X)O_(Y)), silicon carbide (SiC), diamond, and diamond-like carbon.